1. Field of the Invention
This invention relates to microstrip transmission lines and microstrip transmission line components operating in the millimeter wave region of the frequency spectrum and more particularly to a microstrip reciprocal phase shifter for use with such microstrip transmission lines and microstrip components.
2. Description of the Prior Art
Phase shifters are devices employed to perform a phase shift function in many types of RF circuits. For example, in the millimeter wave region of the frequency spectrum phase shifters are employed with phased antenna arrays for radar and communications applications as well as for differential phase shift circulators and switches. Since much of the equipment in this region of the frequency spectrum is designed with planar circuitry utilizing microstrip transmission lines and components, a need has arisen for a suitable microstrip phase shifter capable of being used with this equipment. Although millimeter wave ferrite rod reciprocal phase shifters, such as that shown and described in U.S. Pat. No. 4, 458,218 issued July 3, 1984 to the applicants of the present application and assigned to the assignee of the present application, for example, have been developed for use with millimeter wave frequency applications utilizing the dielectric waveguide medium, there is presently not available a millimeter wave reciprocal phase shifter suitable for use with the aforementioned planar circuitry which uses the microstrip transmission line medium. Since the microstrip transmission components used in applications in this extremely high frequency area of the frequency spectrum are consequently of extremely small size and low weight, they are often difficult to fabricate and assemble using automated techniques. Accordingly, a suitable microstrip phase shifter should be capable of being fabricated relatively easily and inexpensively and of being installed in the planar circuit applications relatively easily and inexpensively to minimize overall equipment cost. Additionally, a suitable microstrip phase shifter should also exhibit a relatively low insertion loss in the millimeter wave region of the frequency spectrum.